Lathe Threading 1/2-20 problem
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  1. #1
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    Default Lathe Threading 1/2-20 problem

    Hello everyone,

    I have been trying to thread a 1/2-20 thread on our Mazak QTU 250.The material is aluminum and the tool I have been using is below:
    266RG-16VM01C001M 1125

    There are two major issues with my finished thread:
    1: There are burrs all over the threads
    2: the finished thread will not thread into the female thread. It might go in half a turn or so and stop. It looks slightly skewed when inside half turn. My "thread identifier" on the other hand goes in goes on without a problem, so I'm assuming my threading is the problem.

    I've had the basic Mazak training which set me up good enough to do the basics. Threading is not given much time at all during that training and I don't have anyone here with a machining background to point me in the right direction so please help. Feel free to be as blunt as necessary, you wont hurt my feelings. I just gotta figure this out.

    The photos below show my program and the thread.

    tensile-program-1.jpgtensile-program-2.jpgtensile-program-3.jpgtenisile-1.jpgtenisile-3.jpg

  2. #2
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    Quote Originally Posted by CallMeShirley View Post
    Hello everyone,

    I have been trying to thread a 1/2-20 thread on our Mazak QTU 250.The material is aluminum and the tool I have been using is below:
    266RG-16VM01C001M 1125

    There are two major issues with my finished thread:
    1: There are burrs all over the threads
    2: the finished thread will not thread into the female thread. It might go in half a turn or so and stop. It looks slightly skewed when inside half turn. My "thread identifier" on the other hand goes in goes on without a problem, so I'm assuming my threading is the problem.

    I've had the basic Mazak training which set me up good enough to do the basics. Threading is not given much time at all during that training and I don't have anyone here with a machining background to point me in the right direction so please help. Feel free to be as blunt as necessary, you wont hurt my feelings. I just gotta figure this out.

    The photos below show my program and the thread.

    tensile-program-1.jpgtensile-program-2.jpgtensile-program-3.jpgtenisile-1.jpgtenisile-3.jpg
    Been a while since i have programmed in Mazatrol.....
    First thing i see is your Angle should be 60 (I believe, referring to the angle of the thread ) and I do not know what the CHFR 2 refers to.....Pretty certain i always left that blank or 0????? Also when using a "topping" insert I would turn to .505"....leaving a little something for the insert to top

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    Refer to MHandbook for the Major dia of the thread. It will be less than 0.5 for sure. And even though the sfpm of 700 won't hurt your tool, you are asking a lot for a threading op. Try something around 250, should still almost be instantanious.

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    No experience with Mazatrol, but at high rpm you could be getting pitch error. As suggested try slowing rpm and check the thread fit then.

  5. #5
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    Quote Originally Posted by Red James View Post
    Refer to MHandbook for the Major dia of the thread. It will be less than 0.5 for sure. And even though the sfpm of 700 won't hurt your tool, you are asking a lot for a threading op. Try something around 250, should still almost be instantanious.
    I have not used that exact insert, but it appears to be a full form topping insert. The diameter should be turned slightly oversize and the insert ends up finishing your major diameter at .495" or so. If you turn it to .495 as you would with a "groove style" insert .....you will end up burred. At that point you may as well save some $ and buy a groove style insert.
    If it is not a full form topping insert I would agree with turning it to .495" or whatever is reccomended.

    You should check your shim as well. That style insert uses a different shim (angled) per diameter to get the angle correct.

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    Sorry if this sounds harsh, but if the thread PD is too big, increase
    the thread height. That's not rocket science. Seems every threading
    insert has a different nose radius, and that effects your thread height.
    Sometimes math nails it first time, sometimes you need to make adjustments,
    MOST of the time you need to make adjustments.

    Also, you are making a wine glass stem, so you in effect are
    giving yourself a shitty L/D ratio. Probably have a lot more
    success by putting the thread on, and then coming in and doing
    the hourglass shape.

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  8. #7
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    I ALWAYS assume I'm going to need to offset the part into tolerance. Every time.

  9. Likes Bobw, Booze Daily, VTM, doug925, Ox and 1 others liked this post
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    I'd try around 300-350rpm, measure the pitch diameter with 3wire or whatever you like and adjust.
    I also like to go back with a finishing tool on the OD to knock any burrs.
    I also turn it to its finish size before threading, about .496" for a 1/2". I don't try to have the insert trim the OD.

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  12. #9
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    I for one running cresting inserts 99% of the time on the OD.


    ---------------------

    Think Snow Eh!
    Ox


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